/diy/ - Do It Yourself

Im using a painters pressure pot to cast resin pieces and since i dont use it too much but still use it I have a bike pump set up and i can get to about 35psi in 30 second. Some of the things i cast are pretty small and dont need all that space in the pot. What would the best materials be to build blocks that take up volume to reduce how much i need to pump? I figure just some wood blocks coated in rubber would do the trick. Any ideas?